In a 10-inch skillet over medium, combine the oil and sausage. Cook, breaking up the sausage and stirring, until browned, 4 to 5 minutes. Using a slotted spoon, transfer to a small plate; set aside.

To the fat remaining in the pan, add the garlic and pepper flakes. Cook over medium, stirring, until fragrant, about 30 seconds. Stir in the tomatoes with juices, oregano and ½ teaspoon each salt and black pepper. Bring to a simmer over medium, then cook, uncovered and stirring, until a spoon drawn through leaves a trail, 15 to 17 minutes.

Meanwhile, heat the broiler with a rack 6 inches from the element. Generously brush both sides of each bread slice with oil and place in a single layer on a broiler-safe rimmed baking sheet. Broil until golden brown on both sides, 2 to 3 minutes, flipping halfway through and rotating the baking sheet for even toasting. Remove from the oven and transfer to a platter.

Add the sausage and any accumulated juices to the tomato mixture, then add about half of the fontina and half of the Parmesan. Return to a simmer over medium and cook, stirring, until the cheese is melted, about 2 minutes. Sprinkle the remaining cheeses over the sauce, then remove from heat. Let stand until melted, about 10 minutes. Sprinkle with basil and serve with the toasts and additional pepper flakes, oregano and Parmesan on the side.