Preheat the oven to 400 degrees F. Toss the serranos, shallot and garlic in some vegetable oil in a small bowl. Season with 1/4 teaspoon salt and a few grinds of pepper. Place on a baking sheet and roast until the vegetables are soft and brown, about 15 minutes. Roughly chop the vegetables and set aside.
Crush the whole cumin seeds using a mortar and pestle. Add the roasted vegetables to the mortar and mash into a smooth paste. Add 2 of the avocados and 1/2 teaspoon salt to the mortar and mash with the vegetables until smooth. Transfer the mixture to a medium bowl. Alternately, pulse the cumin, roasted vegetables, avocados and salt in a food processor.
Roughly chop the remaining 2 avocados and fold them into the smooth avocado mixture. Fold in the lime juice and hot sauce. Season with salt and pepper to taste. Transfer to a serving dish. Serve with tortilla chips.