Finely chop the onions using a food processor or knife.
Slice the cabbage into thin strips. Halve one red pepper, remove seeds, and dice finely. Cut the other red pepper into cubes.
Heat the rapeseed oil in a large pan over medium-high heat. Add the chopped onions and diced pepper, stir-frying for 2-3 minutes until starting to soften.
Add the cabbage strips and season with salt or granulated broth. Stir to combine, cover with a lid, and reduce heat to medium.
After 8 minutes, stir in the cubed pepper and replace the lid.
Continue cooking until the cabbage reaches desired tenderness, about 3-5 minutes more.
Serve as a main course (2-3 plates per person) or as a side dish for more servings.