Tomato rice is less forgiving when treated as an exact universal ratio. Rice varieties, pans, and even how tightly the lid fits change the amount of water lost during cooking.
For two portions, soften a small chopped onion in oil. Stir in a tablespoon tomato paste and cook briefly, then add 150 g long-grain rice. Pour in the amount of water recommended for your rice, allowing for any extra liquid ingredients you add. Season lightly and bring to a simmer.
Cover and cook gently according to the packet, adding a handful of frozen peas near the end with enough time for them to cook through. When the rice is tender, remove from the heat and let it stand covered briefly before fluffing.
If the bottom catches, lift the unburnt rice into a clean serving bowl rather than scraping everything together. Make only what you need when possible; cool and refrigerate any remaining rice promptly, following the dedicated rice-storage note.
Further reading: Food Standards Agency: student food-safety guide.