Preheat oven to 350 degrees F (175 degrees C). Lightly grease 12 muffin cups.
Heat a skillet over medium heat; cook and stir luncheon meat until browned on all sides, about 5 minutes.
Whisk flour, baking powder, baking soda, salt, garlic powder, pepper, and paprika together in a bowl. Mix luncheon meat, milk, Cheddar cheese, butter, spinach, egg, onion, and basil together in a separate bowl; slowly stir into flour mixture just until batter is mixed. Pour batter into muffin cups until each is 3/4-full.
Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, about 33 minutes.
