Prepare the Steak
Heat olive oil in a skillet over medium-high heat.
Season the thinly sliced steak with garlic powder, cumin, smoked paprika, chili powder, salt, and pepper.
Add the steak to the skillet and cook for 4-5 minutes, or until browned and cooked through. Remove the steak from the skillet and set it aside.
Sauté the Vegetables (Optional)
If using bell peppers and onions, add them to the same skillet and sauté for 3-4 minutes, until they soften and begin to caramelize. Remove from the skillet and set aside.
Assemble the Quesadillas
Lay one tortilla flat on a clean surface and sprinkle half of the shredded cheddar and Monterey Jack cheese over one half of the tortilla.
Add a portion of the cooked steak and sautéed vegetables (if using) over the cheese.
Fold the tortilla in half to cover the filling, pressing gently to hold it together. Repeat with the remaining tortillas and ingredients.
Cook the Quesadillas
In the same skillet, melt 1 tablespoon of butter over medium heat.
Place one quesadilla in the skillet and cook for 2-3 minutes on each side, until the tortilla is golden brown and crispy, and the cheese is melted inside.
Repeat with the remaining quesadillas, adding more butter to the skillet as needed.
Serve
Once cooked, remove the quesadillas from the skillet and let them cool for a minute before slicing them into wedges.
Serve with sour cream, guacamole, or salsa on the side for dipping.