Heat 15 ml olive oil in a large, deep frying pan over medium–high heat.
When the oil shimmers, add 450 g lean beef mince and break it up with a spoon. Cook, stirring occasionally, until browned with no pink remaining, about 5–7 minutes. Drain off any excess fat.
Add 1 medium yellow onion, diced, to the pan and cook, stirring frequently, until softened, about 3–4 minutes.
Stir in 2 cloves of minced garlic and cook until fragrant, about 1 minute.
Pour in a 400 g tin of diced tomatoes (including the juices), 360 ml beef stock and 200 g rinsed, uncooked long-grain white rice. Add 1 tsp dried oregano, ½ tsp salt and ¼ tsp black pepper, then stir to combine.
Increase the heat to bring the mixture to the boil.
Reduce to a gentle simmer, cover with a lid and cook until the rice is tender and most of the liquid is absorbed, 15–20 minutes.
If using, stir in 75 g frozen peas for the last 5 minutes of cooking. Alternatively, add them after removing the pan from the heat and leave covered to stand.
Remove the pan from the heat and leave it covered for 5 minutes to rest.
Fluff the rice mixture with a fork and serve piping hot, garnished with chopped fresh parsley and grated cheddar cheese, if you like.