Place the prepared fruit (i.e. bananas, peeled and sliced, strawberries, washed and hulled, etc) in a blender or food processor and puree until the fruit mixture is smooth without an chunks remaining. Transfer the puree to a saucepan and stir in the lemon juice and sugar. Cook the fruit puree over medium to medium high heat for about 10 minutes, stirring frequently to prevent sticking or burning, until the mixture has thickened and the excess moisture cooked out. You’re looking for a jammy consistency.
Preheat the oven to 170 degrees, or as low as your oven will go, making sure it’s less than 200 degrees at the highest. Our oven goes from the ‘warm’ setting to 200, and we found setting it in between those two worked out perfectly.
Spread the puree/jam into a rectangle shape on a baking pan lined with a silpat or with a sheet of parchment paper. Use a spatula to gently help ‘spread’ the fruit puree as evenly as possible, until the rectangle-ish shape is about 1/8 inch thick. Also, as it cooks/dehydrates bear in mind that it will get even thinner, so just try to make sure that none of the jam is so thin that you can see through it as you spread. If using lighter fruits, like peach and mango ours was still see through in a few spots so we tried more to eye ball the thickness and tried to stick close to the 1/8″ mark.
Cook in the oven for 3-4 hours, until the fruit mixture no longer feels sticky, but just a bit tacky. Remove from the oven and let it cool completely. Gently remove the cooked, and now completely cooled, sheet of fruit by peeling it away from the silpat or paper and transfer it to a wax paper lined cutting board. Use a sharp, metal pizza cutter to cut it into long strips. Roll them up into the fruit roll ups, and enjoy!