Place oven rack in center of oven and preheat oven to 400 degrees F; spray heavy, rimmed baking sheet with cooking spray and set aside.
Using a mortar and pestle, or spice grinder, grind the cumin and coriander fine (this can also be done using a plastic bag and a rolling pin or the bottom of a pan).
In a medium skillet, over medium heat, toast the spices until aromatic; place in a small bowl.
Chop the garlic and sprinkle with 1/4 teaspoon salt; using the side of your knife, scrape the garlic and salt to form a paste, then add to the spices.
Also add the remaining 2 teaspoons of salt, pepper, and oil; stir until mixture is smooth.
Place roast on the prepared baking sheet and rub all over with the spice mixture.
Roast in oven until a meat thermometer registers 125 degrees F, for medium-rare, about 35 to 40 minutes.
Transfer meat to a cutting board, tent with aluminum foil, and let rest 20 minutes before carving.
Meanwhile, prepare the mayonnaise: In a small bowl, whisk together the mayonnaise, mascarpone, basil, curry powder, and paprika until mixture is smooth; season with salt and pepper.
Slice meat into 1/4 inch thick slices and arrange on a serving platter; spoon mayonnaise into a small serving bowl and serve alongside.