If you've got any of my other cooking articles here, you know I'm somewhat of a tri tip expert. I love it. Normally, I do mine on the grill, but there are times (especially when I'm busy) where I'll cook it in the oven. And you know what? It still tastes great. Here's how I do it.
First of all, you need to rub / marinade your meat however you like it. There's no perfect way. I've done tri tips all sorts of ways-it's the cut of meat I use when I experiment. However, you're going to want some wet works for the cooking. This could be a mixture of olive oil and other ingredients or your preferred marinade.
If your meat is in the refrigerator, take it out for about 5-10 minutes before cooking.
Heat up your oven to about 425 degrees F. Make note that cooking times and temperatures can vary from oven to oven.
Next, place your tri tip on a baking pan fat side down. Drench a little of your preferred wet works over it and slide it in the middle of your oven. Set your timer for about 45 minutes. Your cooking time might be about 1 hour, but about about the 45 minute mark, you want to pay real close attention to the meat.
Here's the key. Every 8-10 minutes, add some more marinade over the top of your tri tip. You may end up doing this 6-7 times depending on final cooking time. Remember to take it out before it's actually done, because it will continue to cook for up to 10 minutes afterwards. And I like to wrap mine in foil for 5 minutes before cutting it.
Lastly, if your cut of meat has a fair amount of fat on the fat side, start it in the oven with that side up for about 8 minutes and then flip it for the rest of the duration. If you've done everything right, your tri tip from your oven will be very tasty.