Pour oil into a 10- to 12-inch frying pan over medium-high heat. When hot, add onion, garlic, and jalapeños. Stir frequently until onion is limp, 5 to 8 minutes.
In a large bowl, mix crab, spinach, 2 cups cheese, olives, parsley, mayonnaise, Worcestershire, chili powder, cayenne, and onion mixture. Add salt and pepper to taste.
Spread about 1 cup salsa level in a 9- by 13-inch baking dish. Spoon about 1/2 cup of the crab mixture along the center of a tortilla. Roll tortilla around filling. Repeat to fill remaining tortillas, arranging filled tortillas in a single layer over the sauce. Top evenly with remaining 1 cup salsa and remaining 1 cup cheese.
Bake in a 350° oven until cheese is browned and bubbling, about 30 minutes. Let cool in pan about 5 minutes, then serve from pan with a wide spatula.