Heat the olive oil in a large skillet over medium heat.
Add the onion and cook for 2 to 3 minutes until softened.
Stir in the zucchini and bell peppers. Cook for 5 to 6 minutes until tender.
Add the spinach, chili powder, cumin, garlic powder, salt, and black pepper. Cook for 1 minute until the spinach wilts.
Transfer the vegetables to a plate and wipe out the skillet.
Lightly butter or spray the skillet and place one tortilla inside.
Sprinkle half of the tortilla with shredded cheese.
Top with the cooked vegetables, then add another layer of cheese.
Fold the tortilla in half and cook for 2 to 3 minutes per side until golden brown and crispy.
Repeat with the remaining tortillas.
Let the quesadillas rest for 1 minute before slicing into wedges.
Serve warm with salsa, sour cream, guacamole, and fresh lime wedges.