Preheat oven to 350 degrees. Place oven rack on lowest possible position, moving the other racks to make enough room for the pot when ready.
Heat the two cups water and add bouillon cube to dissolve.
Heat olive oil to medium high heat in dutch oven or other lidded oven-ready pot. Season pork roast on all sides with seasoning mix of choice. When pot is ready, add pork roast, browning for a minute or so on each side. Add onion slices, stirring to brown. Add garlic for a minute or so, being careful not to brown, as that would make it bitter.
Pour the water/bouillon mixture into pot and bring to a boil, stirring with wooden spoon to mix in any browned bits on bottom of pot. Bring to a boil, cover tightly and place pot in oven.
Roast for 45 minutes, remove from oven and flip roast. Continue cooking for another 30-45 minutes.
Mix the cornstarch with the remaining 1/2 cup water. Remove pot from oven and onto stove burner on medium heat. Remove roast from pot, adding the cornstarch mixture and whisking until smooth.