Preheat oven to 400 degrees. Bring broth and a pinch of salt to a boil in a small pot. Once boiling, add quinoa. Cover and cook on low heat for 15-20 minutes. Alternatively, you can cook it in the Instant Pot (see notes).
Arrange the pepper halves on a baking sheet and drizzle with 1 Tbsp. olive oil. Sprinkle with salt and pepper. Bake until softened , 7-10 minutes.
Meanwhile, heat 1 Tbsp. olive oil in a large skillet over medium-high heat. Add onions, green onions and garlic, cook for 4-5 minutes, until softened. Add ground beef and break up as it browns, 3-4 minutes. Stir in chili powder, cumin, paprika and cayenne and cook for an additional 30 seconds. Add in tomatoes and let simmer for 5 minutes. Stir in cooked quinoa and season with salt and pepper.
Fill peppers with beef mixture and sprinkle with cheese. Bake 10 minutes. Serve with lime wedges on the side.
Have an Instant Pot? Try cooking your quinoa in there! It's my favorite way to cook quinoa now. Find the simple instructions here.