Preheat the oven to 350F.
In a small pot, melt the butter with the brown sugar, vanilla and salt. Put the oats and flour into a mixing bowl and add the butter-sugar mixture. Drop large spoonfuls 3" apart onto baking sheets that are sprayed with nonstick spray or lined with parchment or a silicone baking mat; with a spatula, spread each cookie out so that it's about 2" in diameter.
Bake for 8-12 minutes, until the cookies are bubbly and golden. Let cool completely on the sheets before removing.