Place broth and rice in 2-quart microwave-safe casserole. Cover tightly and microwave on High until rice is cooked, about 15 minutes.
Whisk egg yolks and lemon juice in medium bowl until blended. Gradually whisk 1 cup hot broth from casserole into egg mixture, then return to casserole and stir to blend. Microwave covered on High until heated through, 1 minute. Season with salt and pepper.
Ladle soup into serving bowls. Garnish with mint and lemon slices; serve hot.