The onions are unfortunate. But it is in the neighborhood of a salad with onions and a raspberry vinaigrette.
I picked up some Quercetin tablets, so I could drop the onion and throw a couple tablets in, but I hate supplements as you never know about the quality control. Dropping the onion and adding apple would make for a pretty tasty drink.
The tough thing is the dose. For the human equivalent of fisetin that was used in this study, you need to eat about 2g of the stuff, which means about 14lbs of strawberries. That's probably a toxic amount of strawberries.