Place all of the steak marinade ingredients in a blender and purée until smooth. Coat the steaks in the marinade and marinate for 4-12 hours.
Preheat the oven to 400°F
On a baking sheet, toss 5 of the garlic cloves, the roma tomatoes and bell pepper with 2 tablespoon olive oil and a pinch of salt and pepper. Roast for 30 minutes, until soft.
Immediately place the peppers in a bowl and cover with plastic wrap. Let them sit for 30 minutes then peel off and discard the skin. Likewise, remove the skins from the roasted tomatoes.
Transfer the roasted garlic, tomatoes and peppers to a food processor, along with the chile powder and paprika and purée until smooth. Add the almonds, bread, remaining 2 raw garlic cloves and purée again. With the machine running, drizzle in the vinegar, oil and lemon juice until smooth. Season with salt and pepper.
Toss the potatoes with the oil, salt, and pepper on a baking sheet. Roast for about 20 minutes, until tender. Cool slightly, then toss with parsley, lemon juice and half of the thyme.
On a second baking sheet, toss the Brussels sprouts with the melted butter, salt and pepper. Roast for 12-15 minutes, until crisp on the edges and soft in the middle. Remove from the oven and toss with the remaining thyme leaves.
Preheat a grill pan or large skillet to high heat with a drizzle of olive oil. Remove the steaks from the marinade, discard excess marinade and pat the steak dry with paper towels. Sprinkle both sides with salt and pepper. Grill the steak for 3 to 4 minutes per side to sear, then lower the heat to medium and cook until an instant-read thermometer reaches 130°F for rare, 140°F for medium rare and 145°F for medium done. Rest for 5-10 minutes before serving.
Brush romesco sauce on plates. Top with roasted potatoes, brussels sprouts and steaks. Sprinkle with flaky salt, black pepper and drizzle with finishing oil.