In a tall pint glass add the instant coffee and brown sugar along with 1/2 cup of warm water. Stir until the coffee and sugar are dissolved.
I love to use a handheld mini milk frother for this step, it creates a thick foam to top your iced coffee.
Add ice to fill the glass 3/4 full, stir the ice into the coffee mixture.
Gently pour 1/2 cup of the oat milk to the coffee mixture in the glass.
Stir to combine and taste. Now you can adjust this to your taste by adding more oat milk or water.
You can also adjust the instant coffee and sugar amounts to your preferences for next time. If you want to adjust these now add them to a little warm water to dissolve them first before adding to the iced coffee.