Step 1 Roast the poblano and red bell peppers on a rack over a gas burner over high heat, turning until the skin is completely charred, about 10 minutes. Cool the peppers in a bowl loosely covered with plastic wrap, then peel and seed.
Step 2 Put the poblano, bell and ancho peppers, serrano chile, olive oil, walnuts, garlic, bread crumbs, pomegranate molasses, cumin, lemon and cilantro in a food processor or blender; puree well.
Step 3Strain the sauce through a medium-mesh strainer and season with 1 1/2 teaspoons salt and a couple grinds of black pepper, or to taste. This will keep, refrigerated, for three days.