Combine 1 teaspoon of the Creole seasoning, 1/2 teaspoon of the thyme, 1/2 teaspoon of the rosemary, 1/4 teaspoon of the garlic powder, and 1/2 teaspoon of the black pepper in a large sealable bag; reserve the remaining half of each spice for later.
Add the thinly sliced top sirloin to the bag and shake or massage until the meat is evenly coated with the spice mixture.
Heat 1 tablespoon canola oil in a large skillet over medium heat, then add the seasoned sirloin and cook, stirring with tongs, until browned, about 2–3 minutes.
Remove the browned steak from the skillet and drain any liquid; wipe the skillet with a paper towel.
Add the sliced red onion and green bell pepper to the skillet along with the remaining reserved seasoning (remaining Creole, thyme, rosemary, garlic powder, and black pepper) and cook until the vegetables are soft, about 3–5 minutes.
Remove the vegetables from the skillet and return the skillet to low–medium heat for assembling the quesadillas.
Place one flour tortilla in the skillet, then evenly arrange 8 provolone slices on the tortilla so most of the surface is covered; cook until the cheese begins to melt.
Spread one third of the cooked steak and one third of the cooked vegetables over half of the tortilla, cook about 2 minutes more, then fold the tortilla in half to form a half-moon and press gently with a spatula.
Cook until the tortilla is golden and the cheese is fully melted, flipping once to brown both sides as needed; repeat assembly for the remaining tortillas and fillings.
Remove quesadillas from the skillet, cut each in half, and serve immediately with desired accompaniments such as salsa or sour cream.