Calabacitas a la Mexicana

Name: Calabacitas a la Mexicana
Ingredients: 1 tablespoon unsalted butter; 1 tablespoon canola oil; 1/2 medium white onion, diced (about 1/2 cup); 1 teaspoon minced garlic; 2 jalapeños, seeded, deveined and finely chopped (about 1/4 cup); 2 summer squash or zucchini (about 12 ounces), diced (about 3 cups); 2 plum tomatoes, diced (about 1 1/4 cups); 2 teaspoons dried Mexican oregano, plus more for serving, optional; Kosher salt and freshly ground black pepper; Sour cream, for serving; Crumbled queso fresco, for serving