Preheat oven to 350. Line a small baking dish with foil, set aside. Cut the onion in half, dice half the onion and slice the other half. Dice the roma tomato. In a small bowl, combine the diced tomato and diced onion. Season with salt and pepper and the juice of half the lime. Set aside. Heat a skillet on medium-high heat with a drizzle of olive oil. Add the sliced onion, stirring and breaking the slices up, cooking until translucent. Stir in the ground beef and brown, stirring to break up and combine with the onion. Season with salt and pepper while cooking. When beef is browned, stir in the tomato paste, the Tex-Mex seasoning and 1/4 c. water. Stir until the sauce is thickened. Remove from heat. Prepare the tortillas, spreading each one with a small amount of olive oil. Fill with meat mixture and a sprinkle of cheese and roll, placing seam side down on foil-lined baking sheet. When all tortillas are rolled, bake for 8-10 minutes until edges start to crisp. While tortillas are baking, mix sour cream together with juice of remaining lime and 1 t. lime zest. Add salt and pepper. Stir until it is a drizzling consistency – you may need to add 1 T. water. When flautas are done baking, remove from oven. Top with limon crema and fresh salsa before serving.