Preheat the oven to 450°F (230°C). Remove the stems from the red bell peppers and slice them in half, removing the seeds. Place them skin-side up on a baking sheet lined with parchment paper and roast until the skins are charred and blistered, about 20 to 25 minutes. Transfer the hot peppers to a bowl and immediately cover it tightly with a lid or an inverted plate for 10 minutes to trap the steam. Once cooled slightly, easily peel off and discard the skins before blending.
Line a rimmed baking sheet with parchment paper or a silicone baking mat. Arrange the walnuts in a single layer on the prepared baking sheet. Toast for 5–7 minutes, stirring occasionally, until fragrant to bring out their rich, earthy flavor. Allow the walnuts to cool completely.
Heat the oil in a skillet over medium heat. Once the oil begins to shimmer, add the onion and cook until softened. Remove from the heat and set aside.
Place the walnuts in a food processor and pulse until coarsely ground. Add the roasted peppers, breadcrumbs, cooked onion along with its oil, cumin, coriander, tahini, and red pepper flakes. Process until the ingredients are well combined.
With the food processor running, gradually add the pomegranate molasses and tahini, processing until the mixture is smooth and well combined. The ingredient quantities have been carefully tested, but feel free to experiment a little! Taste and adjust the seasoning, spiciness, and acidity to suit your preference.