Preheat your oven to 220C/Fan 200/Gas 7. Set a baking tray on the top shelf to heat up. Cut your pepper into 1-2cm slices. Halve, peel and slice your onion about the same width. Toss with 1 tbsp oil. Season. Tumble onto the warmed tray. Roast for 10-15 mins or till a little charred around the edges.
Drain and rinse your beans. Tip into a saucepan with enough water to cover. Simmer 10 mins. Peel your garlic. Add it to the beans half way through their 10 mins. Drain the beans and garlic. Puree in a food processor or blender with the cumin, leaves from a spring of rosemary, 1 tbsp red wine vinegar and a good pinch of salt and pepper.
Whisk the vinegar with 1 tbsp olive oil. Season to taste. Toss the watercress through the dressing.
Paint the butter bean puree on plates to create a bed for the salad. Drizzle a little oil over. Dust with paprika. Toss the roasted pepper and onions with the watercress and pile on top. Finish with a little more paprika and olive oil.