In GIMP do:
Text to path (right click on the text layer to find this)
Path to selection (switch from the layer tab to the path tab and right click on the path to find this)
Select -> Grow (to taste, start with 3-5px)
Select -> Feather (optional, to taste, start with 2-3px)
Create an alpha layer under the text and use the Paint bucket (or just drag the swatch onto the image)
For memes, it might be worth fucking with Inkscape. You can import raster images then add text with a lot of control over stroke / fill / scaling. If you need to do photo touch-up, then you'll need a raster image editor. Krita might be worth looking at if you absolutely can't stand GIMP.