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 cooked through (5–7 minutes). Stir in vinegar; remove from heat.
Veg Mix-In — Stir in kale, roasted red pepper, and finely diced cooked potato. Toss over the residual heat for 1–2 minutes to wilt kale slightly. Cool 2 minutes.
Egg Mixture — In a bowl, whisk 2 eggs until uniform. Stir in chives and lemon zest (if using).
Fill the Cups — Divide the warm sausage-veg mixture evenly among the 8 prepared cups. Pour egg mixture over each, just to moisten and bind (they’ll be quite loaded with filling).
Ricotta “Speckle” — Dot the tops evenly with fat-free ricotta (tiny ¼-tsp dollops) to mimic the white crumble look.
Bake — Bake on the center rack 20–25 minutes, until centers are set and edges lightly golden. Rest 5 minutes before lifting out.