Preheat oven or barbecue to 450°. Place peppers, garlic and onion on a baking sheet or into a barbecue vegetable basket. Place into oven or over barbecue until peppers are charred. Watch the garlic, if it begins to burn remove it and set aside. Burned garlic is not tasty.

Meanwhile gently toast walnuts and pine nuts in a small saucepan over medium heat until brown but not burned, remove from heat.

When peppers are entirely blackened remove them from heat and let cool until you are able to handle them. Peel the charred skins off, remove stem and seeds. Peel the onions and garlic. Transfer all to a blender, add toasted nuts and blend, slowly drizzling olive oil and vinegar into blender until smooth. Season with salt, and more vinegar if desired.

Set aside until ready to use, or refrigerate. You can make this several days ahead, just bring to room temperature before using over your steak.

Finely dice the shallot into a medium sized bowl. Add salt and sweetener and let sit for about 10 minutes, stirring occasionally.

Halve your cherry tomatoes and add to shallots.

Add parsley, tarragon, chopped capers, olive oil and lemon juice. Stir to mix and let sit for at least 1/2 hour. You may refrigerate if making ahead more than a few hours.

Season your lengths of skirt steak generously with salt and pepper. Grill over high heat for 2-3 minutes each side or until done to your preference (these are very thin so watch them, they won't take long!). Remove from grill, let sit for a few minutes and then slice each length ACROSS the grain (this is important for tenderness!)

Place a serving of sliced beef on each plate, add a dollop of romesco and a spoonful of tomato relish to each serving.