In a bowl, beat egg whites with salt until stiff peaks form; set aside. In another bowl, beat the egg yolks, sugar, flour, lemon zest and vanilla until smooth. Fold in egg whites. In a 10-in. ovenproof skillet, melt butter over medium-low heat. Add egg mixture. Cook without stirring for 6-7 minutes or until bottom is golden brown. Remove from the heat. Broil 4 in. from the heat for 1 minute or just until top is golden (watch carefully). Fold omelet in half; transfer to a serving platter. Top with strawberries and whipped cream.