1. Make the romesco: Roast the bell pepper directly over a gas flame or under the broiler, turning often, until charred all over, about 10 minutes. Transfer to a bowl, cover with plastic wrap and let steam for 15 minutes. Peel, core and seed the roasted bell pepper.
2. In a food processor, pulse the roasted pepper with the almonds, garlic, vinegar and crushed red pepper until minced. With the machine on, slowly drizzle in the olive oil until fully incorporated. Season with salt and black pepper.
3. Prepare the scallops and greens: In a large cast-iron skillet, heat 2 tablespoons of the olive oil. Add the scallions, season with salt and pepper and cook over moderately high heat, turning, until lightly charred all over, about 5 minutes. Transfer to plates and wipe out the skillet.
4. Heat 2 more tablespoons of oil in the skillet. Season the scallops with salt and pepper and cook over moderately high heat until golden on the bottom, about 2 minutes. Add the butter, garlic and thyme and flip the scallops.
5. Cook, basting with the butter, until just opaque throughout, about 2 minutes longer. Discard the garlic and thyme. Arrange the scallops on the scallions.
6. In a small bowl, toss the pea tendrils with the remaining 1 tablespoon of olive oil and the lemon juice; season with salt and pepper. Top the scallops with the pea tendrils, garnish with chopped almonds and serve with the romesco.