Frittata with Spinach, Potatoes, Peppers and Feta

INGREDIENTS

2 cups

baby spinach

1 tbsp

olive oil

1 cup

diced red onion (I used much less, about 1/4 cup.)

salt

1 cup

mushrooms, trimmed and sliced

very small (about 3 ounces) russet potato, cut into 1/4-inch cubes (about 1/2 cup)

1/2

red bell pepper, cut into 1/4-inch cubes

large eggs

1/2 cup

crumbled low-fat feta cheese (optional)

1 tsp

dried oregano

1/4 tsp

ground black pepper