Lentil Bolognese with Spaghetti

Heat the olive oil in a large pot or Dutch oven over medium heat until shimmering.
Add the diced onion, carrots, and celery and cook, stirring occasionally, for 8-9 minutes until softened and the onion turns translucent; this vegetable base builds the sauce's depth, so let it fully soften before moving on.
Stir in the garlic and cook for 1 minute until fragrant.
Add the tomato paste and cook, stirring constantly, for 2 minutes until it darkens slightly and smells sweet and toasted, coating the vegetables.
Add the rinsed lentils and stir to coat them in the tomato paste mixture.
Pour in the crushed tomatoes and vegetable broth, then add the oregano, basil, bay leaf, salt, and pepper, stirring to combine.
Bring the sauce to a boil over high heat, then reduce heat to low, cover partially with a lid, and simmer for 30-35 minutes, stirring every 8-10 minutes to prevent sticking.
Check the lentils around the 30-minute mark by tasting a few; they should be fully tender with no hard or chalky center, and the sauce should have thickened to coat a spoon rather than looking watery.
If the sauce is still thin once the lentils are tender, simmer uncovered for another 5-10 minutes to reduce.
While the sauce finishes, bring a large pot of salted water to a boil and cook the spaghetti according to package directions until al dente; drain, reserving 1/2 cup pasta water.
Remove the bay leaf from the sauce and taste, adjusting salt and pepper as needed.
Toss the drained spaghetti directly into the sauce, adding a splash of the reserved pasta water if needed to help it coat evenly.
Serve immediately in bowls, topped with Parmesan if using and a scattering of fresh parsley.