The NoSQL query optimization process is crucial for efficient execution of queries, and the optimizer selects an optimal index and access path to achieve this. However, in MongoDB, the query plan language is simplistic, and the optimizer only supports index selection, not query rewrite or join reordering. The restriction on creating multiple text indexes in MongoDB is due to the inability of the optimizer to validate these indexes against a text predicate, which can lead to performance issues. In contrast, Couchbase's N1QL has added support for text indexes, allowing users to create any number of text indexes and enabling the optimizer to choose a qualified index and use it. This highlights the importance of understanding the query optimization process in NoSQL databases and the need for robust optimization techniques to manage performance issues.