Preheat oven to 450º F.
Place the bell peppers and tomatoes (cut side down) on a baking sheet and roast until charred and softening ~30 minutes. If using cherry tomatoes, leave them whole.
Remove from oven, cover with a kitchen towel and let steam while they cool. Then peel off the red pepper skins and seeds.
Breadcrumbs: use any breadcrumbs you have on hand or lightly oil a couple slices of a baguette and place in the oven with red peppers until crisp (5-7 minutes), let cool, and add to the blender.
While the red peppers and tomatoes are cooking, toast the nuts in a small, dry skillet over medium-low heat, shaking the pan frequently until fragrant and lightly toasted.Remove from heat and let cool. Add the roasted vegetables, almonds, and everything else to the bowl of a food processor. Blend into a coarse sauce stopping to scrape down the sides a required. I leave some texture for a rustic sauce.
Taste and adjust seasonings to your taste. Add more breadcrumbs if needed to thicken the sauce.
Smooth Option: if you prefer a silky smooth romesco sauce, add all ingredients to a blender and blend until smooth.
Cover and store in the fridge in an airtight container for up to a week.