Preheat the oven to 375 degrees F. Line a rimmed baking sheet with foil.
Prep the peppers: Bring a large pot of water to a boil. Carefully drop 4 of the pepper halves into the water and cook for 3-5 minutes (the peppers should be tender but still retain their shape). Use tongs to remove the peppers to a plate and repeat with the remaining 4 pepper halves. Set aside.
In a large nonstick skillet, heat the olive oil over medium-high heat. Add the onion and cook until just beginning to soften, about 2 minutes. Add the garlic and stir for 30 seconds. Add the ground lamb to the pan and cook, breaking it up with a wooden spoon, until no longer pink. Stir in the curry powder, salt, and red pepper flakes, and stir for 30 seconds. Stir in the tomato sauce. Stir in the cauliflower rice. Cook until the mixture has thickened.
Lay the soft pepper halves cut-side-up and use a spoon to divide the lamb mixture among them, stuffing it inside as best you can. Cover the pan with foil and bake for 20 minutes. Uncover and bake for 5 more minutes. Sprinkle the tops with fresh cilantro and a drizzle of plain yogurt. Serve!