Season the chicken cutlets (or fish fillets) on both sides.
In a shallow bowl, combine the flour, garlic powder (or granulated garlic) and paprika. Roll the butter slices in the flour and reserve.
Beat the eggs with the cheese and juice of 1/2 lemon.
In a large, nonstick skillet, heat the oil, four turns of the pan, over medium to medium-high heat. Dredge two pieces of the chicken or fish first in the flour, then coat in the egg batter and cook until golden, 2-3 minutes per side. Transfer to a plate; repeat with remaining cutlets/fillets.
Add the minced garlic to the pan. Stir for 1 minute, then deglaze with the wine (or stock). Add the flour-coated butter and whisk to form a sauce.
Place the chicken or fish on the toasted bun bottoms. Cut the remaining 1/2 lemon into wedges and squeeze over the top. Top with some sauce, arugula, tomato, onion and the bun tops.