Sprinkle gelatin over 1/4 cup cold water in a small bowl. Let sit 5 minutes to bloom.
Heat the juice, tea, or flavored water in a saucepan until hot but not boiling.
Pour the hot liquid over the bloomed gelatin and stir until fully dissolved and smooth.
Whisk the protein powder with the remaining 1/4 cup cold water until smooth.
Let the gelatin mixture cool 2–3 minutes, then slowly whisk in the protein slurry
Stir in stevia and lemon juice if using.
Pour into a muffin tin or small cups.
Refrigerate 2–3 hours until fully set.
Release with a warm knife and serve chilled.