Shred luncheon meat onto a large plate using a cheese grater.
Spray a large skillet with cooking spray and heat over medium-high heat. Add shredded luncheon meat; cook and stir until it begins to brown, about 5 minutes. Stir in taco seasoning and water. Cook and stir until luncheon meat is evenly seasoned and lightly browned, 5 to 7 minutes. Reduce heat to low to keep warm.
Spray another skillet with cooking spray and heat over medium-high heat. Place 1 tortilla in the skillet and cook until heated through, about 30 seconds per side. Repeat with remaining tortillas.
Top warm tortillas with luncheon meat, lettuce, Cheddar cheese, olives, tomato, and onion.