It's probably more Scripps Ranch than Mira Mesa, but it maybe close enough: La Bastide Bistro. They'll have cocktails and apps, but the atmosphere tends to be pretty quiet. I think they only serve their happy hour in the small bar area, not the rest of the restaurant.
Bruski's next to Trader Joe's usually has decent craft beers on tap and burgers.
I can also recommend the Green Flash Brewing's tasting room. They have small tasting glasses of beer for $3/each, some tables (outside only) and usually a food truck parked in the parking lot.
We drove up from San Diego and stayed in an excellent Bed & Breakfast called the Sierra Mountain Lodge in Ahwahnee (about 9 miles outside of Oakhurst).
After reading this board, we had plans to try the Three Sisters and Crab Cakes, but we ended up coming back from Yosemite too late and a little too grimy from hiking each night.
However, we did have a chance to try some perhaps more casual places. Perfect after a day full of long hikes.
I do second other recommendations on this board for El Cid, where our margaritas were strong, the tortilla chips were spicy, and my Machaca with eggs was seasoned just right.
The owner greeted guests at the door and the staff was friendly and attentive.
We also stopped at the Pizza Factory, where our Hawaiian pizza definitely hit the spot.
Perhaps our most unusual find was Ahwahnee's own Hitchin Post, recommended to us by our B&B owners. It's a bar so they're open until 2 am, even on Sundays and the food they serve is high quality and fresh. We had a burger and fish and chips and were impressed with both choices. And it's perfect if you're into getting a little taste of local color. Plus, you don't have to rush back from the park to change and eat.
Perhaps the most disappointing part of our eating experience was the Sunday Brunch at the Ahwahnee Lodge in Yosemite. It's a bit overpriced for what it is, although I suppose it's not bad considering the location, the history of the place, and the amazing dining room. We sat right next to one of the giant windows overlooking the valley floor and I did love the mini fruit tart and creme brulée desserts.
As for those undertaking the long drive from SoCal along the 99, I can recommend a stop at Apple Annie's (in Tulare) if you want to avoid the standard McDonald's pit stop (we got a kick out the toy train doing circles around the ceiling and the boyfriend definitely enjoyed the Ms. Pacman they had in the lobby). I had the Valley Special and a slice of apple pie with apple pie ice cream. I wouldn't necessarily go out of my way to eat there, but it was a good alternative to the chains.