Using the saute function, heat the olive oil in the pressure cooker. When the oil is hot, add the onion and cook until soft. Add the garlic and Italian seasoning and cook another minute until fragrant, then stir in the ground beef and salt. Break the meat into small chunks and saute until cooked through. Stir in the chopped vegetables and canned tomatoes.
Break the spaghetti in half, and place them atop the bolognese mixture, loosely arranging the noodles into two perpendicular layers. Pour in the water, assuring that the noodles are just submerged under the surface (if they are exposed, add another splash of water to cover).
Close the lid, with the valve set to sealing position. Cook on high pressure for 3 minutes.
When the cooking time is complete, carefully open the valve to manually release the pressure. Gently stir to fold the pasta and sauce together, and if the mixture seems wet, let it stands with the lid off for a few minutes and any excess liquid will absorb. Serve topped with fresh herbs and grated Parmesan cheese.