The long strands of spaghetti squash are easily transformed into addictive little croquettes that are crispy on the outside and fluffy in the middle. Serve them as an appetizer or add a salad for a lunch or light dinner.
Preheat the oven to 350 degrees F. Line a rimmed baking sheet with foil.
Drizzle the cut sides of the squash with canola oil and sprinkle with salt and pepper. Put the squash cut-side down on the prepared baking sheet and bake until tender, 50 to 55 minutes. Let cool, then scrape out the stringy flesh with a fork.
Measure out 4 cups of the squash and reserve the rest for another use. Spread the squash on a baking sheet lined with a clean kitchen towel or several layers of paper towel. Place another clean kitchen towel or layer of paper towels on top, then roll up the squash and gently press to remove excess moisture.
Transfer the drained squash to a large bowl. Add the eggs, onion, jalapeno, if using, scallion, cilantro, 2 teaspoons salt and 1/2 teaspoon pepper. Mix well, then stir in 1 cup of the panko. Spread the remaining 1 1/2 cups panko in a shallow dish.
Using a 2-tablespoon scoop, scoop mounds of the mixture onto a baking sheet lined with wax paper. Gently form the mounds into 1/2-inch-thick patties. Coat the patties in the panko, pressing gently to help it adhere, then return them to the baking sheet.
Place a rack over a baking sheet. In a large cast-iron skillet, heat 1/8 inch of oil over medium-high heat. Working in batches, fry the patties, turning once, until browned and crisp, 2 to 3 minutes total. Using a slotted spatula, transfer the croquettes to the rack to drain; sprinkle with salt. Continue frying the remaining patties, adding more oil to the skillet as needed.
Transfer the croquettes to plates or a platter and garnish with chopped cilantro. Serve with sour cream and hot sauce.