Step 1Roast 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 2Put 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.