Prepare Raita: Combine ingredients in a bowl. Season to taste with salt and pepper. Cover with plastic wrap and allow to sit in refrigerator while you prepare the fries (as it sits, the flavor will develop).
Prepare French Fries: Preheat the oven to 425°F (218°C) with a rack in the center position. Line a half sheet pan with parchment paper. Depending on the size of your potatoes, you may need to bake the fries in batches or use a second sheet pan.
Scrub and peel the potatoes. Using a sharp knife, trim ends and slice lengthwise into ¼-inch slices and cut each slice into ¼-inch wide matchsticks. Place in a bowl and cover with cold water. Rinse to remove excess starch. Transfer the potatoes onto a clean kitchen linen and dry thoroughly - pat with additional linens or paper towels as necessary.
Add the oil, cumin, and cayenne pepper in a large mixing bowl or Ziploc half-gallon bag. Add the dry fries and toss until all the french fries are evenly coate in the seasoning.
Carefully transfer the fries to the large baking sheet. Distribute them across the pan, avoiding overcrowding them - you want a little bit of space between each fry - as this will prevent the fries from sticking and help them crisp up in the oven. Season the fries with salt and pepper.
Bake or 15 minutes, flip the fries carefully, and bake for an additional 15 minutes or so. Turn off the oven, keep the fries inside, for an additional 15 to 20 minutes. This step will produce crispier fries. Sprinkle with salt as needed. Serve fries hot with cucumber raita sauce for dipping.