Heat olive oil in a large pot over high heat. Add onion and garlic, cooking for about 1 1/2 minutes until softened.
Add ground beef and cook, breaking it up, until no longer pink.
Stir in the Mexican spice mix and cook for 30 seconds until fragrant.
Add diced capsicum and cook for 1 minute.
Stir in tomato paste and chicken broth until well combined.
Add rice, corn, and black beans. Stir well.
Bring to a simmer, cover, and reduce heat to medium-low. Cook gently for 15 minutes.
Remove lid, stir through green onions and half the cheese.
Smooth the top, sprinkle with remaining cheese, cover, and let sit for 1 minute until melted.
Serve immediately, garnished with extra green onions if desired.