1️⃣ Sauté the spinach filling:
Heat olive oil in a small skillet over medium heat. Add chopped spinach, sprinkle with garlic powder, salt, and pepper. Cook, stirring, until just wilted, about 1–2 minutes. Remove from heat, let cool slightly, then stir in shredded white cheddar.

2️⃣ Prepare the chicken mixture:
In a large bowl, combine ground chicken, minced onion, garlic, Dijon mustard, thyme, paprika, Worcestershire (if using), and a generous pinch of salt and pepper. Mix gently until just combined—avoid over-mixing.

3️⃣ Form and stuff patties:
Divide the chicken mixture into 8 equal portions (≈3 oz each). Flatten one portion into a thin patty in your hand. Spoon about 2 tbsp of the spinach-cheddar filling into the center, leaving a border. Top with another flattened portion and press edges to seal completely, forming a stuffed patty. Repeat for remaining portions.

4️⃣ Chill the patties (optional but helpful):
Place the formed patties on a tray, cover, and refrigerate for 15–20 minutes to help them hold their shape when cooking.

5️⃣ Cook the burgers:
• Grill method: Preheat grill to medium-high. Oil grates. Grill patties 5–6 minutes per side, until internal temp reaches 165 °F (74 °C) and cheese is melted.
• Stovetop method: Heat a little oil in a large skillet over medium heat. Cook patties 6–7 minutes per side, pressing gently, until golden brown and cooked through.

6️⃣ Toast the buns:
In the last minute of cooking, place buns cut-side down on the grill or in the skillet until lightly toasted.

7️⃣ Assemble the burgers:
Spread mayonnaise or aioli on both bun halves. Layer bottom bun with lettuce, a hot spinach-cheddar chicken patty, tomato slice, and red onion rings. Top with the bun crown.

8️⃣ Serve:
Enjoy immediately while the cheese is melty. Serve with sweet potato fries, a green salad, or coleslaw for a complete meal.