In a medium pot, bring 3 c. water and lentils to a boil, reduce heat to simmer and cook about 25 min.
Drain and set aside.
In a small pot, combine vinegar, honey, soy sauce, ginger and ½ c. water.
Bring to a boil.
Meanwhile put cornstarch in a small glass with a little water, mix thoroughly.
Add to boiling sauce to thicken it. Set aside.
In a large skillet, saute onion in 2 T. olive oil.
When onion is soft, add celery and cook for 5 min. over medium heat.
Add cooked, drained lentils to frying pan and mix well.
Pour sweet and sour sauce into frying pan, mix well and simmer for 5 min.
Serve over brown rice or cauliflower rice