Preheat oven to 200/400° C/F.
Line a baking sheet with parchment paper. Add the green beans and fish to the baking sheet. Drizzle with olive oil and sprinkle with salt and pepper to taste. Bake for 15 minutes.
For the romesco, add all of the ingredients except for the olive oil in a food processor. Pulse until finely ground, then with processor on, slowly drizzle in the olive oil until smooth. If too thick, thin out with some water. Add salt and pepper to taste.
Serve fish and green beans topped with romesco sauce.