Preheat your Oven to 350°F. Generously spray a 12 cups Muffin Tin with Cooking Spray, making sure to coat the sides and rims well to prevent sticking.

In a large Mixing Bowl, crack in all 10 10 large eggs and add the ¼ cup whole milk, ½ tsp fine sea salt, ¼ tsp black pepper freshly ground, and ½ tsp garlic powder. Whisk vigorously until the yolks and whites are fully combined and the mixture is slightly frothy, about 1 minute.

Evenly distribute the diced ½ cup red bell pepper finely diced, chopped ½ cup baby spinach roughly chopped, diced ⅓ cup yellow onion finely diced, and crumbled ½ cup cooked turkey sausage crumbled or diced (if using) among the 12 Muffin Tin cups, filling each about one-third full with the veggie and protein mixture.

Rinse peppers under cold water and pat dry. Slice off tops and bottoms, stand upright, and cut down along the inside to remove seeds and white ribs. Slice lengthwise into ½-inch strips; halve crosswise for shorter pieces. Keep sizes uniform so everything cooks evenly. If adding onion, slice it now. Measure out olive oil, salt, and pepper. Have everything ready before the pan goes on — sautéing moves fast.

Heat a large Skillet over medium heat. Add 1 tbsp olive oil per 2 peppers; warm 30–60 seconds until shimmering. Add pepper strips in a single layer — work in batches if crowded. Season with salt and pepper, stir to coat. Cook over medium heat, stirring every 2–3 minutes, for 6–10 minutes. At 6 minutes: slightly softened with snap. At 10 minutes: tender throughout with light color. For very soft peppers, cook 30–40 minutes over medium-low, stirring occasionally. Add garlic halfway through cooking. If browning too fast, add a splash of white wine or water and briefly cover to steam.

Bake in the preheated Oven for 18–22 minutes, until the eggs are fully set in the center and the tops are lightly golden. A toothpick inserted in the center should come out clean. Let cool in the pan for 5 minutes before running a butter knife around the edges to release.