Heat oven to 350ºF. Combine oats, flour, garam masala, baking soda, baking powder and salt in a medium bowl. Set aside.
Beat butter and sugars in a large bowl with an electric mixer on medium speed until thoroughly mixed and creamy. If you're impatient like me and don't let the butter get warm enough before starting, use the tines of a fork to mash it together with the sugar, then finish up with the mixer.
Add eggs, one at a time, and beat until light and fluffy. Add vanilla. Stir in flour mixture until just combined. I usually add it about a third at a time to avoid overwhelming the egg mixture. Stir in raisins.
Using a tablespoon measuring spoon, scoop rounded balls of dough onto greased baking sheets. Flatten slightly. Bake until golden, 12 to 14 minutes [depending on your oven]. Cool on wire racks.