Creamy Shells with Tuna and Spinach

INGREDIENTS

2 cans

each) light tuna in water, light

Yellow onion, small

1/4 cup

All-purpose flour

1/2 tsp

Italian seasoning

1/2 tsp

Red-pepper flakes

Salt and ground pepper, Coarse

3 tbsp

Olive oil, extra-virgin

Hamburger bun

1/4 cup

Parmesan, grated

4 cups

Whole milk

package (10 ounces) frozen chopped spinach, thawed and excess liquid squeezed out