Add 1 tbsp olive oil to the bottom of a large wide pot.
For the onions**: Cut away any roots and remove the first layers of the onion. Then slice the onion down one side, almost to the heart.In a pot, cover onion with water and simmer on medium -low heat, ~10 minutes, until onions are pliable and each onion petal/layer is able to be removed from each other. Drain and set aside to cool.
Once cooled, separate the petals of the onion, one by one. Stuff each petal with ~ 1-2 tbsp of filling and wrap the petal to close.
Place stuffed onions at bottom of pot.
To stuff mini peppers: Slice top of pepper ¾ the way around, see picture. (Keeping the top of the pepper attached will allow the stuffing to remain in the pepper when cooked.)Then, gently core out the seeds within the pepper. Add ~1-2 tbsp of filling until it reaches the top of the pepper. To stuff grape leaves: Remove the grape leaves from the jar. Briefly rinse leaves with water, strain off water.Gently unroll/unfold leaves and lay flat on a clean surface. The smooth side of the grape leaves should be the side touching the surface, the rougher side will have the filling. If there is a stem on the leaf, use a knife to cut around it to fully remove the stem. If the leaf is large, cut vertically in half, as shown in picture. (The vertical edge will now be the base of the newly sized grape leaf.)
Place 1 tsp to 1 tbsp (depending on the size of the leaf) of the stuffing in a log shape toward the bottom of the leaf, near where the stem would attach. Roll the grape leaves by first folding the bottom up, then the right and left sides in then rolling upwards toward the top (see photo), until fully rolled. Do not roll very tightly as the rice will expand when the grape leaves with cooking. Continue to fill and roll each grape leaf this way.
Place rolled grape leaves, seam side down, on top of the onions in the pot. Then place the stuffed peppers. Once complete, all the stuffed vegetables and grape leaf rolls will be layered on top of each other. If there are extra unfilled grape leaves(stems removed), place as the last layer on top of the grape leaf rolls.