Not bioavailability, but rather which amino acids and the ratio of amino acids. If they're not balanced out then one of them becomes the limiting factor. Most modern plant based protein supplements are a blend of proteins that are in balance to avoid that problem, for instance rice and pea blends.
Soy is actually pretty good, very comparable to meat.
Say I had rice for breakfast and peas for lunch - will this be balanced? What if I had them together? Do I need to literally blend them together? Or is it only when they are grown as a same cell it is actually complete protein?
Very probably. The duration scale your body assimilate amino acids together is about 12h-36h IIRC. Most plant eaters I know don’t bother counting anything at all, and the natural craving helps: if I eat a full meal of rice, the peas will be more appealing for the next meal than another bowl of rice. But for taste and texture it’s often better to mix many things in the same meal.
Soy is actually pretty good, very comparable to meat.
Chart and explanation here.
https://en.wikipedia.org/wiki/Protein_quality