Preheat and prep: Preheat your oven to 425°F (220°C). Line a rimmed baking sheet with parchment or foil and set a wire rack on top if you have one (the rack helps the sweet potatoes roast evenly by allowing hot air to circulate). Preheating to a high temperature lets the sweet potatoes caramelize quickly without drying out.

Season the chicken: Pat the 12 oz chicken breasts dry with paper towels (drying promotes a good sear). In a small bowl combine 1 tsp chili powder, 1/2 tsp ground cumin, 1/2 tsp kosher salt (we'll reserve 1/2 tsp of the total salt for the potatoes), 1/8 tsp black pepper, the juice of 1 lime and 1/2 tbsp of the olive oil. Rub this mixture evenly over both sides of the chicken and let it rest at room temperature for 10 minutes while the oven heats. Marinating briefly with acid and oil helps the spices penetrate and brightens the chicken flavor.

Toss and roast the sweet potatoes: In a bowl, toss the 600 g (about 2 med) cubed sweet potatoes with the remaining 1/2 tbsp olive oil, 1/2 tsp kosher salt and a pinch of pepper. Spread them in a single layer on the prepared baking sheet (don’t crowd them — they should sit in a single layer so they can brown). Roast for 20–25 minutes, stirring once halfway through, until the edges are golden and caramelized. Roasting at high heat concentrates the sugars and creates those delicious browned bits.

Rest and sear the chicken: While the sweet potatoes roast, heat a medium nonstick or stainless-steel skillet over medium-high heat until shimmering. Add a light spray of oil or the remaining traces of the seasoning oil in the chicken bowl. Sear the seasoned chicken breasts 3–4 minutes per side until deeply browned for a nice Maillard crust — the sear traps juices and adds flavorful, savory notes. If your breasts are particularly thick (over 1 inch), reduce heat to medium after both sides are browned and cover for 4–6 minutes to finish cooking through. Internal temperature should reach 165°F (74°C).

Rest the chicken: Transfer the chicken to a cutting board and let it rest 5–8 minutes before slicing. Resting allows the juices to redistribute; slicing too soon makes the meat dry.

Slice and dress avocado: While the chicken rests, halve and pit the avocado. Slice it into 1/2-inch slices or dice it, then toss gently with 1 teaspoon lime juice and a light pinch of salt to keep it bright and prevent browning. Acid in the lime juice enhances the avocado’s flavor and adds freshness.

Assemble the bowls: Place 2 romaine leaves per serving (8 leaves makes 4 servings) on each plate to form a shallow bowl. Spoon 1/4 of the roasted sweet potatoes into each, top with sliced chipotle-spiced chicken (slice against the grain for tender bites), 1/4 of the avocado, a few thin slices of red onion, and a sprinkle of chopped cilantro. Finish each with an extra squeeze of lime if desired.

Final seasoning and serve: Taste a bite and add more salt, pepper or lime as needed. Serve immediately while the roasted sweet potatoes are still warm — the contrast of warm sweet potato and cool avocado/lettuce is part of what makes this dish so satisfying.