Drop the garlic, ginger, and jalapeño into a food processor with the motor running. Process till minced. Add the yogurt, sugar, and spices. Pulse until blended. In a bowl, pour the yogurt mixture over the potatoes, squash, zucchini, and onion. Set aside for 20 minutes.
Heat oven to 425º F. Spoon the yogurt-marinated vegetables into a large, shallow roasting pan or jelly-roll pan. Bake 30 minutes, turning once, until all the vegetables are fork-tender. Fold in the peas and cilantro. Serve, refrigerating a third of the vegetables for another use.