Line a baking sheet with parchment paper. Put the flour in a shallow dish and season with salt and pepper. Whisk the eggs and milk in another shallow dish and season with salt and pepper. Combine the breadcrumbs and seeds in a third dish; season with salt and pepper. Lightly dredge each cutlet in the flour, shaking off the excess. Dip in the egg mixture, then in the breadcrumb mixture, pressing to coat both sides.
Arrange the cutlets in a single layer on the prepared baking sheet and refrigerate, uncovered, 1 hour. (This will help the coating stick to the meat.)
Heat the olive oil and butter in a large nonstick skillet over medium-high heat. Working in batches, fry the cutlets until golden brown and crisp, about 3 minutes per side, sprinkling with the parsley during the last minute of cooking. Remove to a rack or paper towel-lined plate to drain. Season with salt.
Sandwich the schnitzel on the pretzel rolls (you might need to cut the bigger pieces of meat). Top with pickles, red onion, lettuce and/or mustard.