carbonel

Fat is flavour.

I don't think the issue is likely to be insufficient flavour inputs; I suspect the issue is likely to be a combination of lean beef and not enough time for the flavours to combine. (Plus zucchini can be a fat mop, which will inhibit the spread of the flavours. A big bland zucchini can blandify its surroundings.)

I'd try heating the sauce back up and giving it half an hour to simmer, stirring a couple tablespoons of olive oil in at the start. If (I'm not sure) you've got the sauce already on spaghetti, I might try the same but adding enough water to be sure it won't stick (and thus burn) while it heats back up, and then time the simmer by how long it takes the sauce to thicken back up as the water boils off.