I just came back from my second trip to Costa Rica in the last few years. Overall, I've found the food there to range somewhere between 'eh' and 'blech' (sorry native Costa Ricans, I know it's supposed to be better on the Caribbean side--just my experience). Don't get me wrong--Costa Rica is a phenomenal travel destination. But usually I plan my vacations around the food and I would say that hasn't been as feasible with Costa Rica. That being said, during my last trip we spent two days at a terrific little lodge along the Sierpe River (between Drake Bay and Palmar Sur) called Sabalo Lodge. The lodge is run by Californian ex-pats Dan and Holly Pesta. Dan is the cook and he made some great stuff while we were there. The lodge is in an extremely remote location and everything has to be brought in by boat, making Dan's culinary feats even more impressive. Unfortunately, I didn't get any pics of the meals, but highlights included a Christmas dinner of smoked turkey with a mushroom sauce, sweet potatoes and Asian green beans with an array of Christmas cookies for dessert and our absolute fave--Snook caught in the river that runs through the lodge cooked in a thai marinade, wrapped in a banana leaf. That would be an actual fresh banana leaf from the premises.
I was quite jealous of what they are able to grow on their property:
Lemongrass:

A variety of herbs/aromatics including turmeric, ginger, galanga (lousy pic, sorry).
They also grow chilis (habaneros)

bananas (and thus banana leaves and blossoms)

If you are heading for the Drake Bay/Corcovado region, I highly recommend a few days at
Sabalo. They can help you arrange the rest of your trip as well.