Heat oven to 275ºF.
Place a cooling rack over a rimmed baking sheet and place in oven to warm.
For the raw sauce, combine the arugula, basil, garlic and lemon juice in a food processor. Season with salt and pepper, and stream in EVOO while food processor runs to form a pesto-like sauce. Toss tomatoes and onions with sauce and reserve.
Pound meat slices to 1/8-inch thick and season with salt and pepper. Set up three shallow dishes for dredging the cutlets: place flour in one with sage, beat eggs in the second and combine breadcrumbs mixed with cheese in the third.
Heat a thin layer of olive oil in a skillet, about 1/4 cup, over medium to medium-high heat.