Finding 4 leaf clovers is one of the things I have a freakish talent for. This bouquet of 15 was picked in about 5 or 6 minutes just after I put one of the bunnies out in their mini-grazing area. And yes, all of them are 4-leaf, but no, this isn't a sign of nuclear waste in my pasture. These were distributed among the bunnies here on the farm that weren't going to get to graze that day.
Rabbits are grazers. As such, they're designed to eat a lot of foliage. Yes, they also like fruit, grain, & veggies, but the overwhelming majority of their diet in nature would generally consist of grasses and foliage. Just read the label on your rabbit feed - what's the first ingredient? Usually alfalfa or similar.
So when the weather is mild, setup a pen in a nice shaded area with clover and tasty looking grasses and weeds, and turn your bunny out for some grazing time. If you haven't been giving your bunn stuff from the yard already, limit the first time out to 15 min or so (longer if they're investigating rather than grazing). First time out, if your bunn is a house bunn, you might also want to keep them in their cage for 12-24 hrs after, just in case they get a bit of loose stool. This is a normal reaction to a sudden introduction of large amounts of fresh, juicy food when they're used to eating hay, generally a result of the natural intestinal flora not being in quite the optimal balance for this food. You can make successive visits longer and eliminate the cage confinement as their intestinal flora adjust to the change in diet.
Just remember to keep watch over your fuzzy friend for their safety and protect them from the heat. They'll enjoy the change of pace and fresh yummy food, and you'll enjoy watching their joy.