Preheat the oven to 250 degrees F. Line a baking sheet with parchment paper. Arrange the tomato slices on the baking sheet. Set the garlic and almonds on and around the tomatoes. Drizzle all with the olive oil; bake 75 minutes.
Place the roasted tomato mixture, ensuring you get all the
juices from the pan, into a food processor. Add the red peppers,
lemon juice and chili flakes, pulse until smooth, and then transfer to a bowl. Cover and refrigerate until needed.
Preheat the oven to 400 degrees F. Place the halibut in a parchment paper-lined baking dish. Drizzle fish with the orange juice; season with salt and pepper. Bake the fish 15 minutes, or until cooked through.
Divide and mound some arugula on each of 4 plates. Set a piece of halibut on the arugula on each plate. Set a dollop of the romesco sauce on each piece of halibut and serve.
Note: Baby arugula is sold in tubs in our produce department. Any leftover romesco sauce can be used the next day as a dip for raw vegetables, or as spread for a sandwich or crostini.