Preheat the oven to 375 degrees F. Whisk the eggs, milk, 3/4 teaspoon salt and a few grinds of pepper in a large bowl until combined; stir in the cheese and set aside.
Heat the olive oil in a 10-inch ovenproof nonstick skillet over medium-high heat. Add the broccoli rabe and garlic and cook, stirring occasionally, until the broccoli rabe is wilted, about 5 minutes. Stir in the pickled peppers and remove from the heat; let cool slightly, then add to the egg mixture and stir.
Wipe out the skillet and return to medium-high heat. Arrange the salami pieces in the skillet in a circle, overlapping slightly, so they cover the bottom. Pour in the egg mixture and cook, without stirring, until the edges start setting, about 1 minute. Transfer the skillet to the oven and bake until the frittata is set and lightly browned, 25 to 30 minutes. Let cool 5 minutes in the skillet, then invert onto a platter or cutting board. Serve warm or at room temperature.