Heat a dry skillet over high heat. Add jalapeños and char, turning occasionally, until blackened on all sides, about 10 minutes. Let cool, then remove stem, seeds, and charred skin. Chop and transfer to a food processor fitted with the blade attachment.

Add mint, cilantro, pumpkin seeds, garlic, salt, and blend. With the processor running add olive oil and lemon juice. Stop blade a few times to scrape down the sides. Blend until very smooth, about 1-2 minutes. Taste and add more salt if needed. If pesto is very thick add a tablespoon or two of hot water to thin out. You want to be able to spoon it over the pumpkin.

Heat a gas or charcoal grill to medium-high. Remove as much peel as you can from the pumpkin with a Y-style vegetable peeler. It's okay if not all of it comes off, pumpkin skin is actually pretty thin and edible. Rub with olive oil and season with salt and pepper.

Grill about 30 minutes or until pumpkin is easily pierced with a fork and is charred on the outside. Turn pumpkin about every 10 minutes or so.

Meanwhile, cook the beans. Heat oil in a small saucepan over medium heat. Add onions and jalapeño. Season with salt and let cook until tender, about 5 minutes, stirring occasionally.

Add garlic, cumin, coriander, and ground arbol chile, and cook a minute more. Add black beans, juices and all and bring to a boil.

Reduce heat to a simmer and let cook until slightly thickened, about 10 minutes. Mash with a potato masher until about 1/2 of the beans are broken up. Taste and add more salt if needed.