Veggie Frittata

Ingredients

• 1 tablespoon butter (extra-virgin olive oil or coconut oil)
• ½ medium yellow onion (finely chopped)
• ½ red bell pepper (finely chopped)
• 1 ½ cups mushrooms (thinly sliced)
• 2 cups kale (chopped)
• 2 cups spinach (chopped)
• 8 eggs
• salt and pepper (to taste)