Shred your blocks of monterey jack and pepper jack cheeses with a cheese grater. Set aside.
In a medium saucepan over medium heat, heat your Ro-tel and green chili salsa.
When the veggies are heated through, add your evaporated milk, cream cheese and seasoned salt. Stir occasionally until everything is melted, combined, smooth and heated through.
Reduce heat to medium-low. Add in your cheeses 1 cup at a time, stirring in between. Mix in all cheese.
Lastly, once your cheese is melted, add your cornstarch/water mixture and stir. Continue stirring occasionally and heating until dip is thickened to your liking. You may need to add a bit more cream cheese or cornstarch to help thicken if it isn't getting thick enough for you.