About the first half of the trip from Morro Bay to Oxnard is off the coast, and while somewhat scenic in a few areas, rolling hills, oak trees, vineyards, nothing to worry about missing. Take 101. Along that route is quaint and farm lands but not freeway speed. 101 comes back on to the coast at Gaviota. Interesting but nothing spectacular like between Moro Bay and Carmel. You will likely see ships in the channel and squid fisherman (lights in the darkness). While there are some interesting sights, in that stretch, nothing to be distressed about missing.
Downtown Ventura has several really nice places to eat on Main St. (much improved since the, appears to be very early, Google street view shots) and we really like Andrias
http://andriasseafood.com/, Brophy's on the other side of the parking lot is said to be could by family members who have eaten there.
No recommendations in Oxnard, we haven't been to any of the places near the marina/harbor. We have a little hole in the wall tacqueria on Saviers we go to. I hesitate to recommend it to someone that isn't a little willing to be daring. It's on the west side of the street, about the 3000 or 3100 block, in a strip mall next to a tortilleria. We've stopped at both when we were "camping" at NAS Pt. Mugu, the first time to get fresh tortillas at the tortilleria and cheap tacos next door. The tacos were as close as I've ever found to the ones they made at my favorite place when growing up, and about $1.25 a great deal. To say they are not fancy, is a gross overstatement. I expect that if you want cheap and authentic Mexican food, almost any of the hole in the wall places in the strip malls will do. Although regretting it the next day, may be a result. Oxnard is primarily agricultural hub and the economy is biased heavily to the local hispanic population except in the beach areas.
Check Sigalert.com for current traffic issues when planning your route from Oxnard to San Diego. They are working on the 5 in the Norwalk area., and the 405 near Seal Beach So I might suggest that you take the 101 to the 134 to the 210 (basically the same freeway, just changes numbers as it goes along) to the 57 to the 5 to get around it, or 101 to 110 or 710 to the 91 or the 405 to get around it You will be staring to the northwest of the "Greater" Los Angeles area and going to the southeast side of it. During rush hour. Some GPS systems get updates for conditions and adjust to them