In a mixing bowl, combine ground beef, egg, almond flour, minced garlic, ginger, cilantro, salt, and pepper. Mix gently with your hands until just combined, don't overwork it.
Roll the mixture into meatballs about 40 g each, roughly golf ball size. You'll get about 14 meatballs.
Heat 1 tbsp coconut oil in a 12-inch skillet over medium-high heat. Sear the meatballs in two batches, 3 to 4 minutes per batch, turning occasionally, until browned on the outside (they won't be cooked through yet). Transfer to a plate.
Add the remaining 1 tbsp coconut oil to the same skillet. Add the onion and cook for 3 to 4 minutes until soft.
Stir in the garlic and ginger and cook for 30 seconds until fragrant. Add the red curry paste and fry for 60 seconds, stirring, until it darkens slightly and smells toasty.
Pour in the coconut milk and chicken broth, stirring to dissolve the paste into the liquid. Bring to a gentle simmer.
Return the meatballs to the skillet and settle them into the sauce. Simmer uncovered for 12 to 15 minutes, spooning sauce over occasionally, until the meatballs reach 160 F / 71 C and the sauce coats the back of a spoon.
Stir in the fish sauce, lime juice, and red pepper flakes if using. Taste and adjust salt.
Garnish with fresh cilantro and serve hot, straight from the skillet.