1. Peel and chop the apples and toss them with the lemon juice to keep them from browning.
2. Peel the rhubarb by taking a paring knife and between your thumb and the knife grab the edge of the outer "skin" and pull it down to allow the skin to peel away. This is not a necessary step but I prefer it done this way because sometimes the outer peel can be a little stringy. Once peeled (or not) chop the rhubarb.
3. Add the apples, orange juice, sugar and cinnamon to a sauce pan.
4. Turn the heat on medium and bring it to a light boil.
5. Turn the heat to medium low and cook, stirring often, until the apples are softened, about 9-10 minutes.
6. Add the rhubarb and continue cooking for another 5 minutes or so until the rhubarb has softened and the sauce has thickened to the desired consistency.
7. Set it aside and let it cool a little bit.