In a small bowl, whisk the mayonnaise, mustard, milk, vinegar, horseradish, sugar, 1/8 teaspoon salt and 1/8 teaspoon pepper. Cover and refrigerate.
In a large saucepan, bring 1/2 in. of water to a boil. Add asparagus; cover and boil for 3 minutes. Drain and immediately place asparagus in ice water. Drain and pat dry. Cover and refrigerate.
Rub steaks with garlic; discard garlic. Sprinkle with remaining salt and pepper. Lightly oil the grill rack.
Grill steaks, covered, over medium heat or broil 4 in. from the heat for 6-8 minutes on each side or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°).
On four serving plates, arrange the greens, tomatoes and asparagus. Thinly slice beef; place over salad. Drizzle with dressing.