Prep all your vegetables by washing, drying, peeling if needed, and chopping into 1/2" or bite-sized pieces. Frozen vegetables do not need to be defrosted.
Warm a skillet over medium heat and add the olive oil. BONUS: if you use a cast iron or other oven-safe skillet, you can make everything in one pan!
Add the onion, sprinkle with a bit of salt, and saute until translucent, anywhere from 5-15 minutes depending on how brown you want your onions.
Add the carrots and potatoes. Sprinkle with a bit of salt, then saute until semi-soft, or about 5 minutes.
Add the rest of your vegetables, a bit of salt, and saute. If you add frozen vegetables, you want them to be completely warmed through before moving on. If you need to drop the heat or add a little more oil, please do.
Once the vegetables feel basically done to you, season with black pepper. Sprinkle the flour over the vegetables, stirring it in to really coat all the produce.
Pour the stock in the pan and stir until there is a nice, shiny consistency. Remove the pan from the heat.