Easy omelet with bell pepper and avocado

Ingredients

• 4 large eggs (240 g)
• ¼ teaspoon salt (1.5 g)
• ¼ teaspoon black pepper (1 g)
• 2 tablespoons unsalted butter (28 g)
• ½ cup bell pepper, diced (75 g; any color)
• 1 ripe avocado, diced (150 g)
• ¼ cup shredded cheese (optional) (30 g; cheddar or mozzarella)