Heat 1 Tbsp. olive oil in a large skillet over medium-high heat. Cook mushrooms until browned, about 3 minutes. Remove to a plate. Reduce heat to medium, and add remaining olive oil to the skillet. Brown Italian sausage, about 3-5 minutes. Add pepperoni and cook 1 additional minute. Stir in marinara sauce mix, diced tomatoes and reserved mushrooms. Bring to a simmer, and cook 5-10 minutes. Warm tortillas or taco shells as directed on the package. Divide sausage mixture among the tortillas or shells, and top with shredded cheese, lettuce, tomato and sour cream. Makes 6 servings.