Prep & Preheat — Heat oven to 375°F (190°C). Line 8 muffin cups with silicone liners or lightly oil.
Make the No-Salt Sausage — Warm olive oil in a nonstick skillet over medium-high. Add turkey, fennel, paprika, garlic powder, onion powder, sage, black pepper, and crushed red pepper (if using). Cook, breaking into small crumbles, until browned and a thermometer reads 165°F (74°C), 5–7 minutes. Stir in vinegar; remove from heat.
Veg Mix-In — Stir in kale, roasted red pepper, and potato. Toss over residual heat 1–2 minutes to wilt kale. Cool 2 minutes.
Egg Mixture — In a bowl, whisk 2 eggs and 3 egg whites until uniform. Stir in chives and lemon zest (if using).
Fill the Cups — Divide the warm sausage–veg mixture evenly among the 8 cups. Pour egg mixture over each just to moisten and bind.
Ricotta “Speckle” — Dot tops evenly with fat-free ricotta (tiny ¼-tsp dollops).
Bake — Bake 20–25 minutes, until centers are just set with a slight jiggle and a knife near center comes out clean, or the egg portion registers ≥160°F (71°C). Rest 5 minutes before lifting out.