Make the dough: on a clean work surface mound 400 g all-purpose flour and make a wide well in the center. Add 175 ml warm water, 2 tbsp olive oil and 1 tsp salt into the well. Mix with your fingers or a fork until the dough comes together — using warm water hydrates the flour faster and helps gluten form without eggs. Knead for 6–8 minutes until smooth and elastic; this develops the gluten that gives the noodles chew and structure. Form a ball, wrap in plastic or cover with a bowl, and let rest for 30 minutes (resting relaxes the gluten so the dough rolls out easily).

Prep the vegetables and chicken: while the dough rests, dice the onion finely, mince the garlic, peel and dice the carrots, core and slice the bell peppers into 1-cm strips, chop the tomato, and cut the potatoes into 1-cm cubes. Pat the 500 g chicken breasts dry and cut into 2-cm pieces. Dry meat browns better — this step ensures a caramelized sear that adds flavor.

Roast the potatoes: toss the potato cubes with 1 tbsp olive oil, 1/4 tsp salt and a pinch of black pepper. Spread on a rimmed baking sheet in a single layer and roast at 220°C/425°F for 20–25 minutes until golden and crisp. Roasting concentrates the potato's starch and creates crispy edges that add textural contrast to the dish.

Roll and cut the pasta: divide the rested dough into 4 pieces. Keep unused pieces covered. Lightly flour your surface and roll one piece at a time to a thin rectangle (3 mm / 1/8 in). Fold the sheet loosely into thirds and cut 6–8 mm (1/4–3/8 in) strips for tagliatelle; unroll the strips and dust lightly with flour so they don't stick. Rolling thin gives the pasta a tender bite that cooks quickly and picks up sauce well.

Dust the chicken and sear: season the chicken pieces with 1/2 tsp salt and a pinch of pepper, then toss with 2 tbsp flour to coat lightly — this helps the chicken brown and also gives the pan juices body for the sauce. Heat a large sauté pan over medium-high heat with 2 tbsp olive oil. Add chicken in a single layer and sear 2–3 minutes without moving until golden, then flip and sear the other side 1–2 minutes. You are building Maillard flavor which is the backbone of the ragù.

Remove the chicken to a plate. In the same pan, add the remaining 1 tbsp oil, then add the diced onion, carrots and a pinch of salt. Sauté on medium heat for 4–5 minutes until the onion is translucent and the carrots have softened slightly — sweating releases their natural sugars and builds the aromatic base of the sauce.

Add minced garlic and sliced peppers and cook 2 minutes until fragrant — you want to soften the peppers but keep some texture. Stir in the chopped tomato, 1 tsp sugar and 1 tsp dried oregano; the sugar helps balance tomato acidity and the oregano gives an Italian herbal note. Scrape any browned bits from the bottom of the pan (those bits carry concentrated flavor).

Return the seared chicken and any accumulated juices to the pan, add 150 ml (about 2/3 cup) water and bring to a gentle simmer. Reduce heat to low and cover partially; simmer 10–12 minutes until the chicken is cooked through and the vegetables are tender. A gentle simmer lets flavors meld without toughening the chicken.

If the sauce seems thin, stir a slurry of the remaining 1 tbsp flour mixed into 2 tbsp cold water, then whisk into the simmering sauce and cook 2–3 minutes to thicken — this yields a silky coating for the pasta. Taste and adjust seasoning with salt and pepper.

Cook the fresh pasta: bring a large pot of salted water to a rolling boil (use about 1 tbsp salt per 4 liters/quarts). Fresh eggless pasta cooks quickly — add the tagliatelle and cook 2–4 minutes until al dente (test one strand). Fresh pasta's short cook time preserves a tender-al-dente texture and avoids sogginess.

Reserve 1 cup (240 ml) of the pasta cooking water, then drain the pasta. Add the drained pasta to the ragù with 1/2 cup (120 ml) of reserved pasta water and toss over low heat for 1–2 minutes until the pasta is thoroughly coated and the sauce clings to the noodles. Pasta water's starch helps emulsify and bind the sauce to the pasta for a glossy finish.

Fold in the roasted potato cubes gently (reserve a few to top each serving for extra crispness). Taste and adjust seasoning. Plate the pasta, spoon extra ragù and potatoes on top, garnish with chopped parsley and a crack of black pepper. Serve immediately.