Measure and rinse (if desired) the quick‑cook steel‑cut oats and have the broth measured nearby. Having everything prepped keeps the timing tight so the oats finish when the toppings are ready.

Bring the 1 1/2 cups (360 ml) vegetable broth to a simmer in a small saucepan over medium heat. Simmering (rather than a rolling boil) reduces evaporation and maintains an even cooking temperature so the oats cook evenly and don’t stick.

Add the oats to the simmering broth, stir once to prevent sticking, reduce heat to low, cover and cook according to package directions for quick‑cook steel‑cut oats (about 8–12 minutes), stirring every 3 minutes. Stirring prevents clumps and helps release the oats’ starches to create a creamy texture.

While the oats cook, warm a medium skillet over medium‑high heat. Add the 1 tsp olive oil and let it heat until it shimmies — hot oil gives the mushrooms a better caramelization instead of stewing.

Add the sliced cremini mushrooms in a single layer and let them sear without moving for 2–3 minutes to develop a golden color. Leaving them undisturbed encourages the Maillard reaction (browning) for deeper flavor.

Stir the mushrooms, season lightly with salt and continue to cook until the liquid released has evaporated and the mushrooms are richly browned, about 3–4 more minutes. Once the moisture reduces, the mushrooms will concentrate in flavor and take on a pleasant chew.

Push the mushrooms to the edge of the skillet, add the minced garlic and cook 30–45 seconds until fragrant (don’t let it burn), then mix with the mushrooms. Garlic added late keeps its fresh aroma and prevents bitterness from overcooking.

Add the baby spinach to the skillet in a handful at a time, seasoning with a small pinch of salt as you add. Toss until wilted, about 1–2 minutes. Cooking spinach briefly preserves its bright color, tender texture and nutrients.

Stir in the halved cherry tomatoes just to warm them through (30–45 seconds) so they keep a little fresh snap. Taste and adjust seasoning with salt and pepper. Warming rather than cooking the tomatoes preserves their brightness and juices.

If the oats are at your preferred tenderness, remove the saucepan from heat. Stir in the optional 1 tsp butter and a pinch of salt to finish the oats — fat and a little salt round out flavor and give silkiness to the bowl.

Divide the creamy oats between two bowls. Top evenly with the sautéed mushrooms, spinach and tomatoes. Scatter the toasted walnuts on top for crunch and finish with fresh herbs, a grind of black pepper and the optional lemon zest to brighten the dish.

Serve immediately while the oats are warm. If desired, offer extra lemon wedges or grated hard cheese (Parmesan or Pecorino) at the table for guests to customize.