Tandoori masala is a mixture of Indian spices used as a rub for meats, poultry or fish which is roasted in a hot, clay tandoori oven. Additionally the spice mixture may be used in a variety of stews and other Indian dishes such as Guchi Mattar.
3 tablespoons coriander seeds
3 tablespoons cumin seed
4 dried red chiles (chile de arbol)
1 teaspoon ajwain seed
2-3 2" pieces of cinnamon stick
10 whole cloves
1 1/2 teaspoon cardmom seeds
2 tablespoons Kashmiri red chili powder (or use 4 teaspoons paprika and 2 teaspoons cayenne powder).
Combine all ingredients except the chili powder in a hot skillet and toast just until they are fragrant. Don't allow the spices to burn. Set the spices aside to cool. Once cool, grind the spices with the chile powder together in a small coffee grinder.
Store the mixture in a small jar with a tight-fitting lid. Makes about 1/3 of a cup.
There are many commercially available brands of tandoori spice available. One of the best brands is Rajh. Look for this spice in Indian grocery stores or online at Amazon.com: Rajah Tandoori Masala.
If you don't have tandoori masala then you have a couple of reasonable options:
If you cook with Indian spices regularly then you probably already have the spices you need to create this mixture. Here is a recipe but like most Indian masalas there are many variations.