Here is the hole in my pants:
Step one was to cut out piece of heavy fusible interfacing (projects like these are a good reason to keep your interfacing scraps) a bit bigger than the hole and ironed it on.
The next thing I did was sew around the edge of the interfacing. Even though in theory the interfacing is now fused in place, let's be real, that stuff doesn't actually stay very well and you don't want those edges coming loose the first time you wash the jeans.
And then you just stitch back and forth over the hole. You can do this from the right or wrong side of the pants. The first time I used this method I was too lazy to get my jeans out from under the pressure foot on my machine after sewing the edges of my interfacing so I sewed from the wrong side.
Pro tip: try not to sew the leg of your pants shut like I did. If you do, no big deal. Just clip those stitches and re-do that part.
Here is what it looked like after I finished fixing my goof-up:
And here is the fixed hole from the right side:
I love this way of fixing jeans. It took all of about five minutes, even with me screwing up and stopping to take pictures, and it requires no hand-sewing. I'm telling you, the gal who came up with this is a genius. It's my go-to for extending the life of my jeans.