Saute onions in 1 ½ cup oil over medium heat until soft. Add rice and all other ingredients. Cook about 20-25 minutes. Cool.
While filling ingredients are cooking, rinse grape leaves in cool water. Pat dry and remove thick stem end.
Working with one leaf at a time, lay the shiny side of the leaf down on a flat work surface. Depending on the size of the leaf, place about 2-3 tsp. of filling on each leaf at the stem end. Fold sides in toward center and roll leaf closed (as if you were making a burrito). Don't roll too tightly as rice expands as it cooks.
Using a large pot, arrange stuffed grape leaves tightly together, stacking on top of each other, until all are arranged. Squeeze lemon juice on top. Put a plate on top of the wrapped grape leaves to help keep them in place while cooking. Pour some water over the grape leaves, but not enough to cover.
Bring to a boil, then reduce heat to low. Cover the pot; cook about 45 minutes until leaves are tender and rice is cooked.