Preheat oven to 450°F. Place a rimmed baking sheet inside the oven to preheat.
Slice each zucchini in half lengthwise. Use a teaspoon to scoop out the center, hollowing slightly. Brush the cut sides with 1 teaspoon of oil.
Carefully place the zucchini cut-side down on the preheated baking sheet and roast for 5 minutes.
Meanwhile, in a large skillet, heat remaining 2 teaspoons of oil over medium-high. Add chorizo, breaking it up with a spoon, and cook until no longer pink, 3 to 4 minutes.
Transfer cooked chorizo to a bowl using a slotted spoon. Add scallions and toss to combine.
Fold in Monterey Jack cheese and chopped cilantro.
Flip zucchini halves cut-side up and season with 1/4 tsp each of salt and pepper.
Divide chorizo mixture among the zucchini (about 1/4 cup per half). Roast for 8 to 10 more minutes until zucchini are tender.
Garnish with more cilantro and serve.