Preheat your oven to 400°F (200°C). Line a rimmed baking sheet with parchment and brush or spray it with olive oil to prevent sticking.
In a large bowl, combine the ground chicken, Parmesan, almond flour, egg, grated onion, garlic, Italian seasoning, salt, pepper, red pepper flakes (if using), and chopped herbs.
Mix gently with a fork or your hands until just combined. Do not overwork the mixture.
Using damp hands or a cookie scoop, form the mixture into about 20 meatballs (roughly 1 1/2 inches in diameter). Space them evenly on the prepared baking sheet.
Bake for 14–16 minutes, or until the centers are just cooked through and the internal temperature reaches 165°F (74°C).
Remove the pan from the oven.
Spoon a little marinara over each meatball, then sprinkle with mozzarella. Switch the oven to broil.
Broil for 2–3 minutes, watching closely, until the cheese is melted and lightly browned. Garnish with extra chopped herbs.
Serve hot with extra marinara on the side.
Great over zucchini noodles, roasted broccoli, or a simple arugula salad with olive oil and lemon.