Preheat oven to 350°F Heat oil in large skillet over medium - high heat. Add asparagus and shallots; cook, stirring until crisp-tender, 4 minutes. Stir in zucchini, thyme and 1/4 tsp salt. Cook, stirring frequently, until veggies soften, 6 minutes.
Coat 4 (6 or 8 oz) custard cups with nonstick spray. Divide vegetable mixture among cups.
Whisk eggs, egg whites, milk, pepper and remaining salt in bowl. Divide egg mixture among cups. Place cups on baking sheet and bake until edges are set, 14 minutes. Sprinkle evenly with cheese. Bake until centers are cooked through, 2 minutes. Cool on rack, 5 minutes.
To travel: cool casseroles, wrap each in plastic wrap and chill up to 3 days. To serve, cut vent in top of one casserole and microwave on medium high until hot. 3 - 4 minutes.
Per serving (1 casserole): 118 cal, 6 g fat, 2 g sat fat, 0 g transfer fat, 141 mg chol, 440 mg sod, 5 g carbs, 3 g sugar, 1 g fib, 10 g prot, 94 mg calc.