Gujarati Eggplant and Sweet Potato Lasagna With Kadi Sauce

Name: Gujarati Eggplant and Sweet Potato Lasagna With Kadi Sauce
Ingredients: A Tomato Masala; 1 pound sweet potatoes, peeled; 1/2 pound eggplant, unpeeled, ends trimmed; 3/4 pound zucchini, ends trimmed; 1/2 large red bell pepper (4 ounces); 1/2 large green bell pepper (4 ounces); 1/4 cup canola oil; 1/2 cup chopped unsalted roasted peanuts; 1 teaspoon salt; 1 cup gram flour (besan); 3 cups water; 1 teaspoon finely chopped fresh ginger; 1/2 teaspoon finely chopped fresh Thai green chile; 1/2 teaspoon ground turmeric; 1 tablespoon whole-milk yogurt; 2 teaspoons salt; 1/4 teaspoon citric acid powder (see Note); Cooking spray; Kadi Sauce, for serving