Marinate the steak. Toss the sliced steak with the minced chipotle peppers, adobo sauce, smoked paprika, garlic powder, cumin, salt, and olive oil. Let it sit for at least 5 minutes (or up to 30 minutes if you have the time).

Cook the steak. Heat a large skillet over medium-high heat. Add the steak in a single layer and cook for 2–3 minutes per side until nicely browned and cooked through. Remove from the pan and set aside.

Sauté the veggies. In the same skillet, cook the red onion and bell pepper over medium heat for 3–4 minutes until softened. Remove and set aside with the steak.

Assemble the quesadillas. Lay a tortilla flat and sprinkle half with a generous layer of cheese. Top with a quarter of the steak and veggie mixture, then add a bit more cheese on top. Fold the tortilla in half.

Cook the quesadillas. Melt ½ tbsp butter in the skillet over medium heat. Add the folded quesadilla and cook for 2–3 minutes per side until golden brown and the cheese is fully melted. Repeat with the remaining tortillas.

Slice and serve. Cut each quesadilla into wedges and serve with your favorite toppings.