I don't know how authentic it is, but it's dang good. Dang good. Start with a wee bit of veggie oil, maybe a teaspoon or so, just enough to coat a cup of long-grain rice. Cook together on medium-high heat until it gets a little toasty, and add a cup of salsa and a cup and a half of chicken broth. Don't bother salting it, the broth and the salsa have plenty of salt already. Crank it to high and bring it to a boil. Give it one last stir, cover (a tight lid is best, but I've used foil in a pinch), and drop to low. Let it sit for 20 minutes, and then turn off the heat. Leave it for another 10 minutes before you open it up. Fluff and serve.
Bonus tips! Instead of cooking in oil, go ahead and use butter. Or, for an other-worldly flavor, slice 3 or 4 strips of bacon into smallish pieces (1/2" or so), fry till almost crispy, drain a little of the fat, and then add the rice. The rice should be ready for the liquids about the same time the bacon really gets crispy. And if you're really looking for a treat, stir in a little shredded cheddar while it's still hot.
The standard ratio for cooking long-grain rice is 1 part rice (by volume) to 2 parts liquid, by volume. If I were making a classic pilaf in cooking school, I might sweat a few veggies in butter before adding the rice. And instead of adding water, I would probably add chicken stock, and maybe even a couple of threads of saffron just for that last bit of elegance. It would make a pretty decent, if somewhat boring pilaf.
Well, it turns out you can't skimp on the water. You might be able to cook rice perfectly well in a smaller amount, but I'm willing to be it just won't be as good. But why did I only use 1 1/2 cups of chicken broth? Because the cup of salsa was really just already cooked veggies, suspended in a really flavorful liquid. I figure in the end it really comes out to 2 cups of liquid, plus maybe a 1/2 cup of veggies.
As for the fat, this is one of those cases where fat is fat. As far as the physics are concerned, you can use whatever fat you want. I understand pork fat might be a little more traditional where they actually make things like Spanish rice, and with the bacon you've got that covered. But butter tastes pretty good too. I'm trying to keep things a little bit healthier, so I just use a nice, neutral veggie oil. And then I like to ruin the health benefits and add a little cheddar. Hey, you have your comfort foods, and I have mine.