Preheat the broiler. In a medium pot of boiling, salted water, parboil the potatoes for 5 minutes; drain.
Pat the beef dry; season with the kosher salt and pepper. Toss with 4 tablespoons EVOO and the garlic and rosemary. Thread as many pieces as will fit on each skewer.
In a large nonstick skillet over medium-high heat, melt the butter with the remaining tablespoon EVOO. Add the potatoes; season with salt, coarse black pepper and paprika. Cook, stirring occasionally, until browned, 10-15 minutes.
Broil the meat on the top rack, turning occasionally, until cooked, about 10 minutes.
In a bowl, make the spiked ketchup: Stir the ketchup with the Worcestershire, horseradish, Tabasco and a pinch of coarse pepper.
Squeeze the lemon over the beef and serve with the greens, crispy potatoes and spiked ketchup alongside.