Preheat the broiler and place the red peppers on a cookie sheet.
Broil the peppers for 3 minutes per side, until the skin is blistered and blackened in places all the way around. This may take up to 20 minutes, depending on how hot the broiler is and how long the peppers take to heat up.
Allow the peppers to cool completely, then peel off the skins and remove the stem and seeds.
Toast the almonds either on a medium-hot skillet or in a 300° oven for 10-15 minutes, until lightly browned and fragrant. Make sure to stir or shake the pan intermittently to prevent the nuts from burning. (If you use slivered almonds, this step will take less time!)
Place the almonds in the food processor and pulse until they reach the texture of coarse sand.
Add the roasted red peppers, garlic, red wine vinegar, salt, and crushed red pepper. Process until the sauce comes together in a smooth puree.
Remove the leaves from the cauliflower and slice it in half through the center. Cut a 1″ thick slice from each half of the cauliflower (i.e., work from the center of the cauliflower head) to make two cauliflower steaks. The rest of the cauliflower can be cut into florets or slices as you wish, but they won't hold together as "steaks."
Rub the cauliflower lightly with olive oil and season with salt and pepper.
Grill the cauliflower steaks and florets over medium-high heat for 3-5 minutes per side, until they can be pierced with a fork and they have grill marks.
Serve the cauliflower with the romesco and fresh herbs (if desired), alongside your favorite bread for dipping!