For marinade, in a small bowl combine vinegar, beer, 2 tablespoons of the fresh marjoram or 2 teaspoons of the dried marjoram, 2 tablespoons oil, the 1/2 teaspoon salt, the 1/2 teaspoon black pepper, and the garlic. Place steak in a resealable plastic bag set in a shallow dish. Pour marinade over steak. Seal bag; turn to coat steak. Marinate in the refrigerator for at least 4 hours or up to 6 hours, turning bag occasionally.
In a covered medium saucepan cook potato wedges in a large amount of boiling water for 4 minutes; drain. In a large bowl stir together potatoes, zucchini, and sweet peppers. In a small bowl stir together 1 tablespoon of the remaining fresh marjoram or remaining 1 teaspoon dried marjoram, 2 tablespoons oil, the 1/4 teaspoon salt, and the 1/4 teaspoon black pepper; sprinkle over vegetables. Toss to coat.
Drain meat, discarding marinade. For a charcoal grill, grill meat, potatoes, zucchini, and sweet peppers on the greased rack of an uncovered grill directly over medium coals until meat is desired doneness and vegetables are tender. Allow 20 to 24 minutes for medium-rare doneness (145 degrees F) or 24 to 28 minutes for medium doneness (160 degrees F), turning meat and vegetables once halfway through grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place meat, potatoes, zucchini, and sweet peppers on grill rack over heat. Cover and grill as above.)
Carve beef across grain into 1/4-inch-thick slices. Arrange beef, potatoes, zucchini, and peppers on serving platter.
Drizzle with half of the Onion Sauce; pass remaining sauce. Sprinkle with remaining fresh marjoram, if using. Makes 6 servings.
In a small saucepan cook onion and bottled minced garlic hot butter over medium heat for 4 minutes or until onions are tender. In a small bowl gradually stir dark beer or dark or amber nonalcoholic beer, beef broth, and Worcestershire sauce into cornstarch. Add to saucepan. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more.