Prepare all the filling ingredients first. Slice the shallots, bell peppers and mushrooms. Remove the pork filet from packaging. First, section the filet into smaller pieces, then slice into thin slices.
Preheat a large frying pan over medium heat and add a bit of olive oil. Saute the sliced pork filet in two batches to avoid overcrowding. Saute each batch for 5 to 6 minutes, until golden brown all over. If using chicken or beef, season the meat with salt, pepper and a sprinkle of paprika.
Remove the pork from the pan into a large bowl and set aside. Into the same pan, add the mushrooms and season them with a pinch of salt; add more olive oil if needed. Saute the mushrooms for a few minutes, then add the shallots and peppers. Continue to saute for a few more minutes, until the peppers are tender.
To assemble the quesadillas, first spread each flour tortilla with a tablespoon of sour cream, then top with a generous amount of mozzarella cheese. Onto one half, add a generous amount of the prepared pork and pepper-mushroom mixture. Drizzle with a tablespoon of your favorite steak sauce. Fold the quesadillas in half and stack until ready to heat.
Heat the quesadillas in a preheated frying pan with a bit of olive oil, or on a grill pan or open-flame outdoor grill. Heat for a few minutes on each side, until the cheese is melted. Serve warm with tomato salsa, sour cream and lime wedges.