Thaw rainbow trout, wash, dry well with kitchen paper and rub / sprinkle with the barbecue seasoning salt on the inside and outside. Peel and dice the onions. Clean, wash and dice tomatoes. Clean, wash and dice the spiced peppers. Clean and wash the celery stalks and cut into rings. Cut the lemon into slices. Put the vegetables in an aluminum dish, place the trout on top, cover with the lemon wedges, drizzle with oil (4 tbsp) and bake / gratinate in the preheated oven at 220 ° C for about 25-30 minutes. Serve the trout with the vegetables. A red wine goes well with it.