Damn You Unity!

public struct Block
{
    // only value types
}

public struct WorldData
{
    public NativeHashMap<int, NativeArray<Block>> ChunkBlocks;

    //ctor with initialization
}

public struct GenerateBlocksForChunksJob : IJobParallelFor
{
    public NativeArray<int> ChunkPositions;

    public NativeHashMap<int, NativeArray<byte>> ChunksBlocksList;

    public void Execute(int index)
    {
        var temp = new byte[Constants.ChunkSize * Constants.ChunkSize * Constants.ChunkSize];
        Vector3Int firstBlockPosition = ChunkPositions[index].ToBlockPosition();

        for (int i = 0; x < temp.Length; i++)
        {
            temp[i] = MagicFunctionToGenerateBlock(i, firstblockPosition);
        }

        ChunksBlocksList[index].CopyFrom(temp);
    }
}


public class World : MonoBehaviour
{
    public Start()
    {
    // computing NativeArray<int> ChunkPositions

    var generateBlocksForChunksJob = new GenerateBlocksForChunksJob()
        {
            ChunksBlocksList = _worldData.ChunkBlocks,
            ChunkPositions = chunkPositions
        };

    // ArgumentException: Unity.Collections.NativeArray`1[System.Byte] used in native collection is not blittable, not primitive, or contains a type tagged as NativeContainer
        generateBlocksForChunksJob
            .Schedule(chunkPositions.Length, 1)
            .Complete();
    }
}