01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with cooking spray or butter.
02 - Heat olive oil in a skillet over medium heat. Add diced potatoes and cook for 5–7 minutes until starting to soften. Add onion and bell pepper; cook for another 3 minutes. Stir in spinach and cook until wilted. Remove from heat and set aside.
03 - In the same skillet, cook diced bacon over medium heat until crisp and browned. Drain on paper towels to remove excess grease.
04 - In a large bowl, whisk together eggs, whole milk, salt, black pepper, and smoked paprika until fully combined and smooth.
05 - Layer the sautéed vegetables, cooked bacon, bread cubes (if using), and half the shredded cheddar cheese in the prepared baking dish. Pour the egg mixture evenly over all ingredients. Top with remaining cheese.
06 - Bake for 35–40 minutes until the eggs are fully set and the top is golden brown. A knife inserted in the center should come out clean.
07 - Let the casserole rest for 5 minutes before serving. Garnish with fresh chives or parsley and serve warm.