Combine olive oil, onion, and ground beef in a skillet over high heat. Cook, stirring, until onion turns translucent and the beef is browned and broken up into very small pieces, about 5 minutes. Add garlic and jalapeno pepper and stir for 2 minutes. Stir in 1 teaspoon salt, chili powder, paprika, cayenne, cumin, dried oregano, cornmeal, and black pepper. Cook for 1 minute more.

Stir in tomato sauce and water and bring to a boil. Reduce heat to medium and simmer, stirring occasionally, until the mixture thickens to your desired texture, 5 to 10 minutes. Remove from heat and set aside to cool.

Use a teaspoon or melon baller to scoop out about half the center of each zucchini to create a “boat.” Sprinkle generously with remaining kosher salt and let sit, 15 to 20 minutes.

Meanwhile, preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with a silicone liner.

Use a paper towel to blot any moisture that the salt draws out of the zucchini. Place boats on the prepared baking sheet and fill each one with as much taco meat mixture as will fit. Top evenly with pepper Jack cheese.

Bake in the preheated oven until the cheese is browned and the zucchini is just barely tender, about 20 minutes. Test for doneness with a sharp knife. Serve immediately.