Heat the olive oil in a large pot over medium-high heat. Add onion, carrots, celery and salt and stir to coat with oil. Cook for about 5 minutes, stirring occasionally, until beginning to soften. If you happen to get distracted and the veggies brown a little bit, it'll add some nice depth of flavor.
Stir in stock, bring to a boil, then cover and reduce heat to simmer until veggies are tender. Remove lid and add spinach and tortellini. Cook according to tortellini package instructions (usually just simmering for a couple of minutes). Off the heat, stir in parsley and black pepper to taste.
Ladle into bowls and serve with cheese to pass at the table.
As you may know by now, this is by far my favorite vegetable stock.